In gas turbine engine operation it is known to bleed off high pressure air, known as P3 air, from a diffuser of a compressor into an impeller rear cavity, downstream of the centrifugal impeller for the purpose of loading the impeller and thus removing stress on the adjacent bearings. However, such pressurized air is generally at a high temperature and tends to degrade the impeller hub, thereby reducing the effective lifespan of the impeller. In order to reduce the degradation effect on the impeller, it has been contemplated to use high heat resistant materials which, however, will increase the cost of the impeller while providing a weaker impeller hub more susceptible to fractionating under high centrifugal forces. Bypass air may be used to cool the P3 air entering the impeller rear cavity. However, this cooling method may present other issues and is even not applicable in gas turbine engines which do not produce bypass air such as turboprop or turboshaft engines.
Accordingly, an improved system and method for cooling an impeller of gas turbine engines is required.